This invention generally relates to variable capacity pumps and, more particularly, to centrifugal pumps with impeller sections which are axially adjustable to vary the pump flow rate.
Centrifugal pumps are normally designed to operate at high efficiency over a predetermined operating range with a reduction in pump efficiency occurring as such pumps deviate from the design flow conditions. For example, a reduction in pump efficiency due to partial loading often becomes acute at relatively low flow demands with attendant internal recirculation of pump fluid, pump overheating, fluid pressure pulsations, and undesirable hydraulic noise. Attempts to produce a pumping system that can efficiently and quietly vary its flow and pressure characteristics to match varying system demands have included plural pump arrangements, pump throttling and bypass techniques, and utilization of variable geometry pumps. One form of variable flow centrifugal pump includes axially adjustable impeller sections for varying the flow rate of the pump, as exemplified, for example, by U.S. Pat. Nos. 3,407,740; 3,771,927; 3,806,278; 3,901,623; 3,918,831; and 4,070,132. In these pumps, the impeller sections are keyed to the rotor shaft with various spline means so that relative rotational displacement of the impeller sections is precluded as the axial spacing between adjacent impellers is increased. However, axial movement of the impeller sections while under load often results in high friction and related wear problems. Since the tolerances between different parts of the pump are normally quite critical to ensure high pump efficiency, abrasive wearing of various elements of this type of pump structure results in erratic operation of the impeller parts, decreasing pump efficiency, increased maintenance costs, and production of undesirable hydraulic noise.